U.S. patent application number 16/734006 was filed with the patent office on 2021-07-08 for fuel tank inerting system and method.
The applicant listed for this patent is Hamilton Sundstrand Corporation. Invention is credited to Haralambos Cordatos, Zissis A. Dardas, Sean C. Emerson, Matthew Robert Pearson, Rajiv Ranjan, Ying She, Eric Surawski.
Application Number | 20210206503 16/734006 |
Document ID | / |
Family ID | 1000004582918 |
Filed Date | 2021-07-08 |
United States Patent
Application |
20210206503 |
Kind Code |
A1 |
Dardas; Zissis A. ; et
al. |
July 8, 2021 |
FUEL TANK INERTING SYSTEM AND METHOD
Abstract
A system is disclosed for inerting a fuel tank. The system
includes a fuel tank and an air separator including a membrane with
a permeability differential between oxygen and nitrogen, an air
inlet and an inert gas outlet in fluid communication with a first
side of the membrane, and a sweep gas inlet and an oxygen-enriched
gas outlet in fluid communication with a second side of the
membrane. An inert gas flow path is arranged to receive inert gas
from the air separation module oxygen-depleted air outlet, and to
direct inert gas to the fuel tank. A catalytic reactor is arranged
to receive a fuel and air, and configured to catalytically react
the fuel and oxygen in the air to form an oxygen-depleted gas, and
to discharge the oxygen-depleted gas from a reactor outlet. A sweep
gas flow path from the reactor outlet to the air separator sweep
gas inlet.
Inventors: |
Dardas; Zissis A.;
(Worcester, MA) ; Emerson; Sean C.; (Broad Brook,
CT) ; She; Ying; (East Hartford, CT) ; Ranjan;
Rajiv; (South Windsor, CT) ; Cordatos;
Haralambos; (Colchester, CT) ; Pearson; Matthew
Robert; (Hartford, CT) ; Surawski; Eric;
(Hebron, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hamilton Sundstrand Corporation |
Charlotte |
NC |
US |
|
|
Family ID: |
1000004582918 |
Appl. No.: |
16/734006 |
Filed: |
January 3, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B64D 37/14 20130101;
B60K 2015/03348 20130101; B60K 2015/03236 20130101; B60K 15/03
20130101; B64D 37/32 20130101 |
International
Class: |
B64D 37/14 20060101
B64D037/14; B64D 37/32 20060101 B64D037/32; B60K 15/03 20060101
B60K015/03 |
Claims
1. A fuel tank inerting system for an aircraft, comprising: a fuel
tank; an air separator comprising a membrane with a permeability
differential between oxygen and nitrogen, an air inlet and an inert
gas outlet in fluid communication with a first side of the
membrane, and a sweep gas inlet and an oxygen-enriched gas outlet
in fluid communication with a second side of the membrane; an inert
gas flow path arranged to receive inert gas from the air separation
module oxygen-depleted air outlet, and to direct inert gas to the
fuel tank; a catalytic reactor arranged to receive a fuel and air,
and configured to catalytically react the fuel and oxygen in the
air to form an oxygen-depleted gas, and to discharge the
oxygen-depleted gas from a reactor outlet; and a sweep gas flow
path from the reactor outlet to the air separator sweep gas
inlet.
2. The system of claim 1, further comprising a cooler arranged to
cool inert gas generated by the catalytic reactor.
3. The system of claim 1, further comprising an air flow path from
a compressed air source to an inlet of the air separator.
4. The system of claim 3, wherein the air flow path is between an
aircraft engine compressor section and the inlet of the air
separator.
5. The system of claim 1, wherein the catalytic reactor, or an air
source for the catalytic reactor, or an oxygen-depleted gas flow
path from the catalytic reactor to the sweep gas inlet, or any
combination of the foregoing are configured to provide a pressure
at the sweep gas inlet that is above a pressure at the
oxygen-enriched gas outlet and below a pressure on the first side
of the air separator membrane.
6. The system of claim 1, wherein the sweep gas inlet and the
oxygen-enriched gas outlet are arranged to provide co-flow with air
flow on the first side of the air separator membrane.
7. The system of claim 1, wherein the sweep gas inlet and the
oxygen-enriched gas outlet are arranged to provide counter-flow
with air flow on the first side of the air separator membrane.
8. The system of claim 1, wherein the sweep gas inlet and the
oxygen-enriched gas outlet are arranged to provide cross-flow with
air flow on the first side of the air separator membrane.
9. A method of operating the system of claim 1, comprising:
directing air to the air separator air inlet; transporting oxygen
from air on the first side of the air separator membrane to the
second side of the air separator membrane to form an inert gas on
the first side of the air separator membrane and an oxygen-enriched
gas on the second side of the membrane; directing inert gas from
the air separator inert gas outlet to the fuel tank; reacting fuel
with oxygen in air in the catalytic reactor to produce an
oxygen-depleted gas, and directing the oxygen-depleted gas from the
catalytic reactor to the air separator sweep gas inlet; and
outputting oxygen-enriched gas from the air separator
oxygen-enriched gas outlet.
10. The method of claim 9, wherein fuel is reacted with oxygen in
the catalytic reactor to produce oxygen-depleted gas continuously
throughout operation of the membrane separator.
11. The method of claim 9, wherein fuel is reacted with oxygen in
the catalytic reactor to produce oxygen-depleted gas in response to
a demand for inert gas.
12. A method of producing an inert gas, comprising. separating air
through a membrane with a permeability differential between oxygen
and nitrogen to produce the inert gas on a first side of the
membrane and oxygen-enriched air on a second side of the membrane;
catalytically reacting a fuel with oxygen to produce an
oxygen-depleted gas; and directing the oxygen-depleted gas as a
sweep gas to the second side of the membrane.
13. A method of inerting a fuel tank, comprising producing an inert
gas according to the method of claim 12, and directing the inert
gas to the fuel tank.
14. The method of claim 13, wherein fuel is reacted with oxygen to
produce oxygen-depleted gas continuously throughout separation of
air through the membrane.
15. The method of claim 13, wherein fuel is reacted with oxygen to
produce oxygen-depleted gas in response to a demand for inert gas.
Description
BACKGROUND
[0001] The subject matter disclosed herein generally relates to
systems for generating and providing inert gas, oxygen, and/or
power on aircraft, and more specifically to fluid flow operation of
such systems.
[0002] It is recognized that fuel vapors within fuel tanks become
combustible or explosive in the presence of oxygen. An inerting
system decreases the probability of combustion or explosion of
flammable materials in a fuel tank by maintaining a chemically
non-reactive or inert gas, such as nitrogen-enriched air, in the
fuel tank vapor space, also known as ullage. Three elements are
required to initiate combustion or an explosion: an ignition source
(e.g., heat), fuel, and oxygen. The oxidation of fuel may be
prevented by reducing any one of these three elements. If the
presence of an ignition source cannot be prevented within a fuel
tank, then the tank may be made inert by: 1) reducing the oxygen
concentration, 2) reducing the fuel concentration of the ullage to
below the lower explosive limit (LEL), or 3) increasing the fuel
concentration to above the upper explosive limit (UEL). Many
systems reduce the risk of oxidation of fuel by reducing the oxygen
concentration or by introducing an inert gas such as
nitrogen-enriched air (NEA) (i.e., oxygen-depleted air or ODA) to
the ullage, thereby displacing oxygen with a nitrogen or other
inert gases at target thresholds for avoiding explosion or
combustion.
[0003] It is known in the art to equip vehicles (e.g., aircraft,
military vehicles, etc.) with onboard inert gas generating systems,
which supply an inert gas to the vapor space (i.e., ullage) within
the fuel tank. Various systems have been used or proposed for
generating inert gas onboard an aircraft, and each system imposes
its own fuel consumption burden vehicle based on various criteria
including but not limited to the consumption of compressed air,
consumption of electricity, demand for ram air, payload of system
components, and combinations including any of the foregoing. Each
of the systems that have been used or proposed has its own
potential advantages and disadvantages, and there continues to be a
demand for technical solutions for the provision of inert gas
onboard aircraft.
BRIEF DESCRIPTION
[0004] A system is disclosed for inerting a fuel tank. The system
includes a fuel tank and an air separator including a membrane with
a permeability differential between oxygen and nitrogen, an air
inlet and an inert gas outlet in fluid communication with a first
side of the membrane, and a sweep gas inlet and an oxygen-enriched
gas outlet in fluid communication with a second side of the
membrane. An inert gas flow path is arranged to receive inert gas
from the air separation module oxygen-depleted air outlet, and to
direct inert gas to the fuel tank. A catalytic reactor is arranged
to receive a fuel and air, and configured to catalytically react
the fuel and oxygen in the air to form an oxygen-depleted gas, and
to discharge the oxygen-depleted gas from a reactor outlet. A sweep
gas flow path from the reactor outlet to the air separator sweep
gas inlet.
[0005] In some aspects, the system can further include a cooler
arranged to cool inert gas generated by the catalytic reactor.
[0006] In addition to, or as an alternative to, any one or
combination of the above features, the system can further include
an air flow path from a compressed air source to an inlet of the
air separator.
[0007] In addition to, or as an alternative to, any one or
combination of the above features, the air flow path can be between
an aircraft engine compressor section and the inlet of the air
separator.
[0008] In addition to, or as an alternative to, any one or
combination of the above features, the catalytic reactor, or an air
source for the catalytic reactor, or an oxygen-depleted gas flow
path from the catalytic reactor to the sweep gas inlet, or any
combination of the foregoing can be configured to provide a
pressure at the sweep gas inlet that is above a pressure at the
oxygen-enriched gas outlet and below a pressure on the first side
of the air separator membrane.
[0009] In addition to, or as an alternative to, any one or
combination of the above features, the sweep gas inlet and the
oxygen-enriched gas outlet can be arranged to provide co-flow with
air flow on the first side of the air separator membrane.
[0010] In addition to, or as an alternative to, any one or
combination of the above features, the sweep gas inlet and the
oxygen-enriched gas outlet can be arranged to provide counter-flow
with air flow on the first side of the air separator membrane.
[0011] In addition to, or as an alternative to, any one or
combination of the above features, the sweep gas inlet and the
oxygen-enriched gas outlet can be arranged to provide cross-flow
with air flow on the first side of the air separator membrane.
[0012] Also disclosed is a method of operating a system including
any one or combination of the above features. According to the
method, air is directed to the air separator air inlet, and oxygen
is transported air on the first side of the air separator membrane
to the second side of the air separator membrane to form an inert
gas on the first side of the air separator membrane and an
oxygen-enriched gas on the second side of the membrane. The
oxygen-enriched gas is outputted from the air separator
oxygen-enriched gas outlet, and the inert gas is directed from the
air separator inert gas outlet to the fuel tank. Fuel is reacted
with oxygen in air in the catalytic reactor to produce an
oxygen-depleted gas, and the oxygen-depleted gas is directed from
the catalytic reactor to the air separator sweep gas inlet.
[0013] In some aspects, the method can include reacting the fuel
with oxygen in the catalytic reactor to produce oxygen-depleted gas
continuously throughout operation of the membrane separator.
[0014] In addition to, or as an alternative to, any one or
combination of the above features, fuel can be reacted with oxygen
in the catalytic reactor to produce oxygen-depleted gas in response
to a demand for inert gas.
[0015] Also disclosed is a method of producing an inert gas.
According to the method, air is separated through a membrane with a
permeability differential between oxygen and nitrogen to produce
the inert gas on a first side of the membrane and oxygen-enriched
air on a second side of the membrane. Fuel is catalytically
reacting with oxygen to produce an oxygen-depleted gas, and the
oxygen-depleted gas is directed as a sweep gas to the second side
of the membrane.
[0016] In some aspects, a method of inerting a fuel tank can
include separating air through a membrane with a permeability
differential between oxygen and nitrogen to produce an inert gas on
a first side of the membrane and oxygen-enriched air on a second
side of the membrane, reacting fuel with oxygen to produce an
oxygen-depleted gas, and directing the oxygen-depleted gas as a
sweep gas to the second side of the membrane, and directing the
inert gas to the fuel tank.
[0017] In some aspects of the method of inerting a fuel tank, fuel
is reacted with oxygen to produce oxygen-depleted gas continuously
throughout separation of air through the membrane.
[0018] In addition to, or as an alternative to, any one or
combination of the above features, the method of inerting a fuel
tank can include reaction of fuel with oxygen to produce
oxygen-depleted gas in response to a demand for inert gas.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The following descriptions should not be considered limiting
in any way. With reference to the accompanying drawings, like
elements are numbered alike:
[0020] FIGS. 1A and 1B are schematic illustrations of different
views of an aircraft;
[0021] FIG. 2 is a schematic illustration of a membrane air
separator;
[0022] FIG. 3 is a schematic illustration of a portion of a fuel
tank inerting system including a catalytic reactor in accordance
with an embodiment of the disclosure; and
[0023] FIG. 4 is a schematic illustration of a fuel tank inerting
system including an air separator and a catalytic reactor in
accordance with an example embodiment of the disclosure.
DETAILED DESCRIPTION
[0024] A detailed description of one or more embodiments of the
disclosed apparatus and method are presented herein by way of
exemplification and not limitation with reference to the
Figures.
[0025] FIGS. 1A-1B are schematic illustrations of an aircraft 101
that can employ one or more embodiments of the present disclosure.
As shown in FIGS. 1A-1B, the aircraft 101 includes bays 103 beneath
a center wing box. The bays 103 can contain and/or support one or
more components of the aircraft 101. For example, in some
configurations, the aircraft 101 can include environmental control
systems and/or fuel inerting systems within the bay 103. As shown
in FIG. 1B, the bay 103 includes bay doors 105 that enable
installation and access to one or more components (e.g.,
environmental control systems, fuel tank inerting systems, etc.).
During operation of environmental control systems and/or fuel tank
inerting systems of the aircraft 101, air that is external to the
aircraft 101 can flow into one or more environmental control
systems within the bay doors 105 through one or more ram air inlets
107. The air may then flow through the environmental control
systems to be processed and supplied to various components or
locations within the aircraft 101 (e.g., passenger cabin, fuel
inerting systems, etc.). Some air may be exhausted through one or
more ram air exhaust outlets 109.
[0026] Also shown in FIG. 1A, the aircraft 101 includes one or more
engines 111. The engines 111 are typically mounted on wings of the
aircraft 101, but may be located at other locations depending on
the specific aircraft configuration. In some aircraft
configurations, air can be bled from the engines 111 and supplied
to environmental control systems and/or fuel tank inerting systems,
as will be appreciated by those of skill in the art.
[0027] Aspects of the function of fuel tank flammability reduction
systems in accordance with embodiments of the present disclosure
can be accomplished by separating oxygen from nitrogen in air
utilizing a membrane with a permeability differential between
oxygen and nitrogen. An example embodiment of a membrane separator
is shown in FIG. 2. FIG. 2 depicts a tubular membrane, but other
configurations such as planar membranes can also be used. As shown
in FIG. 2, a tubular membrane 20 comprises a tubular shell 22. The
membrane 20 can be fabricated from a material that has selective
permeability to oxygen compared to nitrogen such that a pressure
differential across the membrane provided by a gas comprising
nitrogen and oxygen on the high-pressure side of the membrane will
preferentially diffuse oxygen molecules across the membrane. For
ease of illustration, the membrane 20 is depicted as a monolithic
hollow shell, and membranes fabricated solely out of the selective
oxygen-permeable membrane material are included within the scope of
this invention. However, in many cases, the membrane is a composite
of a substrate or layer that is permeable to both oxygen and
nitrogen and a substrate or layer that is selectively permeable to
oxygen.
[0028] The shell 22 defines a hollow core 26 that is open at both
ends. In use, pressurized gas comprising nitrogen and oxygen (e.g.,
air which is known to also contain trace amounts of noble/inert
gases) is delivered into the hollow core 26 at an inlet end 27 of
the membrane 20. The pressure of the air is greater than air
outside the core 26 such that a pressure differential between the
hollow core 26 and air at the exterior 24 of the membrane 20
exists. Oxygen molecules preferentially diffuse through the tubular
membrane 20 compared to nitrogen molecules, resulting in a flow of
oxygen-enriched air (OEA) from the outer surface of the tubular
membrane 20 as shown in FIG. 3, and a flow of nitrogen-enriched air
(NEA) from the hollow core 26 at the outlet end 28 of the membrane
20 as shown in FIG. 2. An alternative mode of operation for the
membrane is to maintain equal or nearly equal pressure on each
side, but utilize a carrier gas (sweep gas) on the back side of the
membrane such that the partial pressure of the gas to be removed is
always higher on the top side of the membrane, thereby providing
the driving force for separation. The membrane 20 can be formed
from different materials, including but not limited to polymers
(e.g., polyimides, polysulfones, polyketones (e.g., PEEK),
polycarbonates) including polymers of intrinsic microporosity
("PIM") (e.g., polybenzodioxanes) and thermally-rearranged ("TR")
polymers (e.g., thermally-rearranged polybenzoxazoles), or
refractory ceramics (e.g., zeolite).
[0029] As mentioned above, a catalytic reactor can be utilized to
produce an oxygen-depleted gas as a sweep gas for a membrane air
separator. Such a reactor performs catalytic reaction of a fuel
(e.g., a "first reactant") with a source of gas containing oxygen
such as air (e.g., a "second reactant"). The product of the
reaction is carbon dioxide and water vapor. The source of the
second reactant (e.g., air) can be bleed air or any other source of
air containing oxygen, including, but not limited to, high-pressure
sources (e.g., engine), bleed air, cabin air, etc. A catalyst
material such as a noble metal catalyst is used to catalyze the
chemical reaction. The conversion of oxygen in the air feed to
carbon dioxide and water via the catalytic reaction produces an
oxygen-depleted gas.
[0030] The catalytic chemical reaction between fuel and air also
generates water. Water in the fuel tank can be undesirable. Thus,
in accordance with embodiments of the present disclosure, the water
from a product gas stream (e.g., exiting the catalyst) can be
removed through various mechanisms, including, but not limited to,
condensation. The product gas stream can be directed to enter a
heat exchanger downstream from the catalyst that is used to cool
the product gas stream such that the water vapor condenses out of
the product gas stream. The liquid water can then be drained
overboard. In some embodiments, an optional water separator can be
used to augment or provide water separation from the product
stream.
[0031] Aircraft fuel tanks are typically vented to ambient
pressure. At altitude, pressure inside the fuel tank is very low
and is roughly equal to ambient pressure. However, during descent,
the pressure inside the fuel tank needs to rise to equal ambient
pressure at sea level (or at whatever altitude the aircraft is
landing). This change in pressure requires gas entering the tank
from outside to equalize with the pressure in the tank. Outside air
entering the fuel tank can provide oxygen for combustion of the
fuel, and the systems disclosed herein can provide an inert gas to
the fuel tank to help reduce the risk of combustion.
[0032] FIG. 3 is a schematic illustration of a flammability
reduction or inerting system portion 200 utilizing a catalytic
reaction between first and second reactants to produce inert gas in
accordance with an embodiment of the present disclosure. The
inerting system portion 200, as shown, includes a fuel tank 202
having fuel 204 therein. As the fuel 204 is consumed during
operation of one or more engines, an ullage space 206 forms within
the fuel tank 202. To reduce flammability risks associated with
vaporized fuel that may form within the ullage space 206, an inert
gas can be generated and fed into the ullage space 206.
[0033] The inerting system portion 200 utilizes the catalytic
reactor 222 to catalyze a chemical reaction between oxygen (second
reactant 218) and fuel (first reactant 216) to produce carbon
dioxide-containing for the inert gas (inert gas 234) and water in
vapor phase (byproduct 236). The source of the second reactant 218
(e.g., oxygen) used in the reaction can come from any source on the
aircraft that is at a pressure greater than ambient, including but
not limited to bleed air from an engine, cabin air, high pressure
air extracted or bled from an engine, etc. (i.e., any second
reactant source 220 can take any number of configurations and/or
arrangements), and as disclosed in more detail hereinbelow includes
a membrane air separator. Even non-air oxygen sources can be used,
and "air" is used herein as a short-hand term for any
oxygen-containing gas. The fuel (first reactant 216) is provided by
pressurizing fuel 204 from the fuel tank 202 with a pump 210 and
atomizing it in an injector 214. The atomized fuel (first reactant
216) from the injector 214 can be mixed with second reactant 218 in
a mixing zone 224 and delivered to the catalytic reactor 222 as
shown in FIG. 3, or the reactants 216, 218 can each be directly
delivered to the reactor.
[0034] With continued reference to FIG. 3, the mixed reactant
stream 225 (e.g., fuel and oxygen or air) is then introduced to the
catalytic reactor 222, catalyzing a chemical reaction that
transforms the mixed reactant stream 225 (e.g., fuel and air) into
the inert gas 234 and the byproduct 236 (e.g., water vapor). It is
noted that any inert gas species that are present in the mixed
reactant stream 225 (for example, nitrogen from the air) will not
react and will thus pass through the catalytic reactor 222
unchanged. In some aspects (not shown), the catalytic reactor 222
can be include heat exchange components for rejection of heat from
the catalytic reactor 222 to a heat sink.
[0035] The catalytic reactor 222 can be temperature controlled to
ensure a desired chemical reaction efficiency such that an inert
gas can be efficiently produced by the inerting system portion 200
from the mixed reactant stream 225. Accordingly, cooling air 226
can be provided to extract heat from the catalytic reactor 222 to
achieve a desired thermal condition for the chemical reaction
within the catalytic reactor 222. The cooling air 226 can be
sourced from a cool air source 228. A catalyzed mixture 230 leaves
the catalytic reactor 222 and is passed through a heat exchanger
232. The heat exchanger 232 operates as a condenser on the
catalyzed mixture 230 to separate out an inert gas 234 and a
byproduct 236 (e.g., water). A cooling air is supplied into the
heat exchanger 232 to achieve the condensing functionality. In some
embodiments, as shown, a cooling air 226 can be sourced from the
same cool air source 228 as that provided to the catalytic reactor
222, although in other embodiments the cool air sources for the two
components may be different. The byproduct 236 may be water vapor,
and thus in the present configuration shown in FIG. 3, an optional
water separator 238 is provided downstream of the heat exchanger
232 to extract the water from the catalyzed mixture 230, thus
leaving only the inert gas 234 to be provided to the ullage space
206 of the fuel tank 202. In some embodiments, the inerting system
portion 200 can supply inert gas to multiple fuel tanks on an
aircraft. After the inert gas 234 is generated, the inert gas 234
will flow through a fuel tank supply line 256 to supply the inert
gas 234 to the fuel tank 202 and, optionally, additional fuel tanks
258.
[0036] A flow control valve 248 located downstream of the heat
exchanger 232 and optional water separator 238 can meter the flow
of the inert gas 234 to a desired flow rate. An optional boost fan
240 can be used to boost the gas stream pressure of the inert gas
234 to overcome a pressure drop associated with ducting between the
outlet of the heat exchanger 232 and the discharge of the inert gas
234 into the fuel tank 202. The flame arrestor 242 at an inlet to
the fuel tank 202 is arranged to prevent any potential flames from
propagating into the fuel tank 202.
[0037] Typically, independent of any aircraft flammability
reduction system(s), aircraft fuel tanks (e.g., fuel tank 202) need
to be vented to ambient pressure. Thus, as shown in FIG. 2, the
fuel tank 202 includes a vent 250. At altitude, pressure inside the
fuel tank 202 is very low and is roughly equal to ambient pressure.
During descent, however, the pressure inside the fuel tank 202
needs to rise to equal ambient pressure at sea level (or whatever
altitude the aircraft is landing at). This requires gas entering
the fuel tank 202 from outside to equalize with the pressure in the
tank. When air from outside enters the fuel tank 202, water vapor
can be carried by the ambient air into the fuel tank 202. To
prevent water/water vapor from entering the fuel tank 202, the
inerting system portion 200 can repressurize the fuel tank 202 with
the inert gas 234 generated by the inerting system portion 200.
This can be accomplished by using the valves 248. For example, one
of the valves 248 may be a flow control valve 252 that is arranged
fluidly downstream from the catalytic reactor 222. The flow control
valve 252 can be used to control the flow of inert gas 234 into the
fuel tank 202 such that a slightly positive pressure is always
maintained in the fuel tank 202. Such positive pressure can prevent
ambient air from entering the fuel tank 202 from outside during
descent and therefore prevent water from entering the fuel tank
202.
[0038] A controller 244 can be operably connected to the various
components of the inerting system portion 200, including, but not
limited to, the valves 248 and the sensors 246. The controller 244
can be configured to receive input from the sensors 246 to control
the valves 248 and thus maintain appropriate levels of inert gas
234 within the ullage space 206. Further, the controller 244 can be
arranged to ensure an appropriate amount of pressure within the
fuel tank 202 such that, during a descent of an aircraft, ambient
air does not enter the ullage space 206 of the fuel tank 202.
[0039] The catalytic reactor 222 can be temperature controlled to
ensure a desired chemical reaction efficiency such that an inert
gas can be efficiently produced by the inerting system portion 200
from the mixed reactant stream 225. Accordingly, cooling air 226
can be provided to extract heat from the catalytic reactor 222 to
achieve a desired thermal condition for the chemical reaction
within the catalytic reactor 222. The cooling air 226 can be
sourced from a cool air source 228. A catalyzed mixture 230 leaves
the catalytic reactor 222 and is passed through a heat exchanger
232. The heat exchanger 232 operates as a condenser on the
catalyzed mixture 230 to separate out an inert gas 234 and a
byproduct 236 (e.g., water). A cooling air is supplied into the
heat exchanger 232 to achieve the condensing functionality. In some
embodiments, as shown, a cooling air 226 can be sourced from the
same cool air source 228 as that provided to the catalytic reactor
222, although in other embodiments the cool air sources for the two
components may be different. The byproduct 236 may be water vapor,
and thus in the present configuration shown in FIG. 3, an optional
water separator 238 is provided downstream of the heat exchanger
232 to extract the water from the catalyzed mixture 230, thus
leaving only the oxygen-depleted gas 234 to be provided as a sweep
gas to a membrane separator module 404 through flow path 256.
[0040] A flow control valve 248 located downstream of the heat
exchanger 232 and optional water separator 238 can meter the flow
of the inert gas 234 to a desired flow rate. An optional boost fan
240 can be used to boost the gas stream pressure of the inert gas
234 to overcome a pressure drop associated with ducting between the
outlet of the heat exchanger 232 and the discharge of the inert gas
234 into the fuel tank 202. The flame arrestor 242 at an inlet to
the fuel tank 202 is arranged to prevent any potential flames from
propagating into the fuel tank 202.
[0041] Typically, independent of any aircraft flammability
reduction system(s), aircraft fuel tanks (e.g., fuel tank 202) need
to be vented to ambient pressure. Thus, as shown in FIG. 3, the
fuel tank 202 includes a vent 250. At altitude, pressure inside the
fuel tank 202 is very low and is roughly equal to ambient pressure.
During descent, however, the pressure inside the fuel tank 202
needs to rise to equal ambient pressure at sea level (or whatever
altitude the aircraft is landing at). This requires gas entering
the fuel tank 202 from outside to equalize with the pressure in the
tank. When air from outside enters the fuel tank 202, water vapor
can be carried by the ambient air into the fuel tank 202. To
prevent water/water vapor from entering the fuel tank 202, the
inerting system portion 200 can repressurize the fuel tank 202 with
the inert gas 234 generated by the inerting system portion 200.
This is accomplished by using the valves 248. For example, one of
the valves 248 may be a flow control valve 252 that is arranged
fluidly downstream from the catalytic reactor 222. The flow control
valve 252 can be used to control the flow of inert gas 234 into the
fuel tank 202 such that a slightly positive pressure is always
maintained in the fuel tank 202. Such positive pressure can prevent
ambient air from entering the fuel tank 202 from outside during
descent and therefore prevent water from entering the fuel tank
202.
[0042] A controller 244 can be operably connected to the various
components of the inerting system portion 200, including, but not
limited to, the valves 248 and the sensors 246. The controller 244
can be configured to receive input from the sensors 246 to control
the valves 248 and thus maintain appropriate levels of inert gas
234 within the ullage space 206. Further, the controller 244 can be
arranged to ensure an appropriate amount of pressure within the
fuel tank 202 such that, during a descent of an aircraft, ambient
air does not enter the ullage space 206 of the fuel tank 202.
[0043] An example embodiment of an inert gas generating system 400
including a membrane separator and a catalytic reactor is
schematically shown in FIG. 4. Fluid flows between the components
in FIG. 4 through the arrowed lines that are described contextually
below unless explicitly identified and numbered. As shown in FIG.
4, air from an air source 402 (which can be the same as or
different from an air source use as a second reactant source 220)
is directed first to an inlet 403 of the membrane separator module
404 with membrane 20' that can be formed from bundles of tubular
membranes such as shown in FIG. 3. The air source 402 can include
any source on the aircraft that is at a pressure greater than
ambient, including but not limited to bleed air from an engine,
cabin air, high pressure air extracted or bled from an engine, etc.
Other components (not shown) can be disposed along the air flow
path 403 between the air source 402 and the membrane separator
module inlet 403. For example, in the case of a gas turbine engine
compressor section air source, the hot compressed air can be
directed to a heat rejection side of a heat exchanger to be cooled
to a temperature suitable for the membrane. Other components can
also be included upstream of the membrane separator module 404,
including but not limited to one or more filter components,
including but not limited to a particulate filter (e.g., a HEPA
filter) for removal of particulates, or a coalescing filter for
removal of liquid entrained in the air flow. In the case of
multiple filter components, they can be integrated into a single
module or can be disposed in separate modules (not shown) on the
air flow path. Other air treatment modules can be included upstream
of the membrane separator module 404, including but not limited to
catalytic treatment modules such as for ozone removal.
[0044] With continued reference to FIG. 4, air from the air source
402 is transported from a first side of the membrane 20' across the
membrane to produce an oxygen-enriched gas on a second side of the
membrane 20', which is discharged from oxygen-enriched gas outlet
406, from where it can be exhausted off-board or can be directed to
an on-board system for further utilization. A sweep gas in the form
of oxygen-depleted gas from an outlet 223 of the catalytic reactor
222 is directed along a sweep gas flow path 401, and introduced to
the second side of the membrane 20' through a sweep gas inlet 405.
Oxygen-depleted air discharged from is directed from an outlet 407
of the membrane separator module 404 along an inert gas flow path
408 to the ullage space 206 of fuel tank 202. In some aspects, the
sweep gas inlet 405 and the outlet 406 can be arranged to provide
co-flow of the sweep gas (left to right in FIG. 4) with respect to
a direction of flow of gas on the first side of the membrane 20'.
In some aspects, the sweep gas inlet 405 and the outlet 406 can be
arranged to provide counter-flow of the sweep gas (right to left in
FIG. 4) with respect to a direction of flow on the first side of
the membrane 20'. In some aspects, the sweep gas inlet 405 and the
outlet 406 can be arranged to provide cross-flow of the sweep gas
(bottom to top in FIG. 4) with respect to a direction of flow on
the first side of the membrane 20'.
[0045] In operation, aircraft fuel tanks are typically vented to
ambient pressure. At altitude, pressure inside the fuel tank is
very low and is roughly equal to ambient pressure. However, during
descent, the pressure inside the fuel tank needs to rise to equal
ambient pressure at sea level (or at whatever altitude the aircraft
is landing). This change in pressure requires gas entering the tank
from outside to equalize with the pressure in the tank. Outside air
entering the fuel tank can provide oxygen for combustion of the
fuel, and the systems disclosed herein can provide an inert gas to
the fuel tank to help reduce the risk of combustion.
[0046] The system 400 or variants on the system 400 can be operated
in different modes of operation. For example, in some aspects, the
flow of sweep gas from the catalytic reactor 222 can be adjusted by
the controller 244 in response to a demand for inert gas, with
higher flow rates of or lower oxygen levels of the sweep gas
provided in response to higher levels of demand for inert gas.
During aircraft descent, the system demand for inert gas can be
relatively high because increasing outside atmospheric pressure
tends to force outside air into the fuel tank through the vent
system, and a greater volume of inert gas is needed in order to
displace outside air or prevent inflow of outside air. However,
under other operating conditions such as cruise or aircraft ascent,
the system demand for inert gas can be relatively low since only
the volume from fuel consumption must be replaced as there is no
pressure-driven inflow of outside air.
[0047] In some aspects, the above-described system configuration
and modes of operation can provide a technical effect of promoting
more effective separation of oxygen from nitrogen by a membrane due
to the effect of lower partial pressure of oxygen in the sweep gas
providing a greater differential in oxygen pressure across the
membrane. This can reduce or eliminate the need for pressurized air
such as bleed air from the engine as an air source for the membrane
separator 404. For example, one could use cabin air exhaust (which
is in plentiful supply) in conjunction with an electrically driven
blower, thereby reducing fuel burn consumption. Additional benefits
can also be achieved, such as reduction in membrane size (e.g.,
shorter length tubular membranes) and design capacity reductions of
the air separator 404 compared to prior systems that use only
membrane separators. The catalytic reactor 222 and its associated
components can also be sized smaller compared to prior proposed
systems that use only catalytic reaction of fuel to produce inert
gas, and can achieve significantly reduced fuel consumption
compared to systems that catalytic reactor systems that would
operate throughout flight operations.
[0048] As discussed in various aspects above and shown in FIGS. 3
and 4, the systems disclosed herein can include a controller 244.
The controller 244 can be in operative communication with the air
separator 404, the catalytic reactor 222, and any associated
valves, pumps, compressors, conduits, ejectors, pressure
regulators, or other fluid flow components, and with switches,
sensors, and other electrical system components, and any other
system components to operate the inert gas system. These control
connections can be through wired electrical signal connections (not
shown) or through wireless connections. In some embodiments, the
controller 244 can be configured to operate the system according to
specified parameters, as discussed in greater detail further above.
The controller can be an independent controller dedicated to
controlling the inert gas generating system, or can interact with
other onboard system controllers or with a master controller. In
some embodiments, data provided by or to the controller 244 can
come directly from a master controller.
[0049] The term "about" is intended to include the degree of error
associated with measurement of the particular quantity based upon
the equipment available at the time of filing the application.
[0050] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the present disclosure. As used herein, the singular forms "a",
"an", "the", or "any" are intended to include the plural forms as
well, unless the context clearly indicates otherwise. It will be
further understood that the terms "comprises" and/or "comprising,"
when used in this specification, specify the presence of stated
features, integers, steps, operations, elements, and/or components,
but do not preclude the presence or addition of one or more other
features, integers, steps, operations, element components, and/or
groups thereof.
[0051] While the present disclosure has been described with
reference to an exemplary embodiment or embodiments, it will be
understood by those skilled in the art that various changes may be
made and equivalents may be substituted for elements thereof
without departing from the scope of the present disclosure. In
addition, many modifications may be made to adapt a particular
situation or material to the teachings of the present disclosure
without departing from the essential scope thereof. Therefore, it
is intended that the present disclosure not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this present disclosure, but that the present
disclosure will include all embodiments falling within the scope of
the claims.
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